The present invention relates to pumps, and more particularly to pumps having sealless shafts.
Pumps are used in a wide variety of applications to transport various types of materials. Centrifugal pumps, for example, are typically used to transport fluids. Such pumps are adapted for use with a motor having a rotating motor shaft, and generally include a housing defining a pump chamber, a fluid inlet, a discharge outlet, and a shaft opening. An impeller shaft is attached to the motor shaft, extends through the shaft opening in the pump housing, and has an end disposed inside the pump chamber. An impeller is attached to the impeller shaft so that, as the impeller rotates, fluid is drawn through the inlet and discharged through the outlet.
Such pumps typically include a seal at the shaft opening in the pump housing to prevent fluid from leaking along the impeller shaft. Such seals are typically provided in the form of a gasket, such as an o-ring, which is attached to the shaft opening and engages the impeller shaft. Conventional gasket seals, however, create a number of problems. Not only do the gasket seals themselves wear out, but the seals also cause wear on the impeller shafts. Such seals do not tolerate a shaft which rotates with a wobble or some other type of eccentricity, and the seals generate heat due to friction between the stationary seal and rotating impeller shaft. In addition, gasket seals rapidly wear out and fail when the pump is operated dry (i.e., when pump chamber is not filled with fluid). Furthermore, all gasket seals leak to some extent, regardless of seal material or tightness.
In one application, a centrifugal pump is incorporated into a vacuum cleaner. Tank-type vacuum cleaners have an air impeller disposed inside a tank which is capable of vacuuming dry materials such as debris or dirt and suctioning liquids into the tank. When the tank is full, the pump removes liquid from a lower portion of the tank and expels it through a hose to waste. As taught in commonly owned U.S. patent application Ser. No. 09/281,671now U.S. Pat. No. 6,119,304, the air and pump impellers are advantageously connected to a common shaft which is rotating by a single motor. The air and pump impellers are mounted proximate one another in an upper portion of the tank, near the motor. As a result, it is important to prevent fluid from leaking through the shaft opening and into the air impeller and motor. It is also desirable, however, to use the vacuum produced by the air impeller to prime the pump.
In the above-referenced vacuum cleaner, a liquid deflector is positioned between the pump and air impeller to prevent fluid from reaching the air impeller and motor. In addition, the distance between the pump and the air impeller is increased, thereby lengthening the shaft. As a result, while these modifications adequately prevent fluid from reaching the air impeller and motor, the vacuum cleaner requires additional components, making assembly more difficult and expensive. Furthermore, the longer impeller shaft increases the likelihood of vibration and thus noise and additional wear on the shaft support bearings.
To utilize the vacuum produced by the air impeller to prime the pump, the impeller shaft is formed with a bore leading to an impeller backing plate formed with spacers, so that a path is formed from the air impeller, through the shaft, and to the pump chamber. A vacuum director is attached to the impeller shaft to further ensure that the vacuum is communicated to the shaft and ultimately to the pump chamber. Accordingly, the components used in the above vacuum cleaner are overly intricate and complex to assemble, and the weight supported by the rotating impeller shaft is overly excessive.
In accordance with one aspect of the present invention, a pump for transporting fluid is provided which is adapted for use with a motor having a rotating motor shaft. The pump comprises a pump housing having an inlet opening, an outlet opening, and a shaft opening, the pump housing defining a pump chamber. An impeller shaft has a first end adapted for connection to the motor shaft and a second end disposed inside the pump chamber, and the impeller shaft extends through the shaft opening in the pump and is sized to define a gap between the impeller shaft and the shaft opening. An impeller assembly is disposed inside the pump chamber and is attached to the second end of the impeller shaft. The impeller assembly includes a first set of impeller blades located near the inlet and outlet openings of the pump housing for drawing the fluid through the inlet opening and discharging the fluid through the outlet opening, and a second set of impeller blades located near the shaft opening of the pump housing for creating a pressure force which pushes fluid away from the shaft opening, thereby preventing fluid from leaking through the gap.
In accordance with another aspect of the present invention, a vacuum cleaner is provided which is adapted for attachment to a rotating motor shaft. The vacuum cleaner comprises a tank having an inlet for receiving liquid material and defining an interior. An impeller shaft is adapted for attachment to the rotating motor shaft, and a pump housing defines a pump interior and has an inlet opening, an outlet opening, and a shaft opening sized to receive the impeller shaft. A gap is defined between the shaft opening and the impeller shaft. A pump impeller is disposed inside the pump interior and is attached to the impeller shaft. The pump impeller includes a first set of impeller blades located near the inlet and outlet openings of the pump housing, and a second set of impeller blades located near the shaft opening of the pump housing. A pump inlet is disposed in the interior of the tank and is in fluid communication with the inlet opening of the pump housing, wherein the pump inlet places the interior of the pump in fluid communication with the interior of the tank. An air impeller assembly is disposed in air flow communication with the interior of the tank. The air impeller assembly includes a housing and a driven air impeller disposed in the housing, the housing defining an opening in air flow communication with the interior of the tank. The driven impeller creates a relatively low pressure area in the interior of the tank. A priming apparatus is in fluid communication with the pump interior, and means for establishing a pressure differential across liquid in the priming apparatus is provided thereby to prime the pump.
In accordance with yet another aspect of the present invention, a vacuum cleaner is provided which is adapted for attachment to a rotating motor shaft. The vacuum cleaner comprises a tank having an inlet for receiving liquid material and defining an interior. An impeller shaft is adapted for attachment to the rotating motor shaft, and a pump housing defines a pump interior and has an inlet opening, an outlet opening, and a shaft opening sized to receive the impeller shaft. A gap is defined between the shaft opening and the impeller shaft. A pump impeller is disposed inside the pump interior and is attached to the impeller shaft. The pump impeller includes a first set of impeller blades located near the inlet and outlet openings of the pump housing, and a second set of impeller blades located near the shaft opening of the pump housing. A pump inlet is disposed in the interior of the tank and is in fluid communication with the inlet opening of the pump housing. The pump inlet places the interior of the pump in fluid communication with the interior of the tank. An air impeller assembly is disposed in air flow communication with the interior of the tank and includes a housing and a driven air impeller disposed in the housing. The housing defines an opening in air flow communication with the interior of the tank and the air impeller defines an interior space. The driven air impeller creates a relatively low pressure area in the interior of the tank and in the interior space defined by the air impeller. A priming apparatus is disposed between the air impeller and the pump, wherein the priming apparatus places the interior of the pump in air flow communication with the low pressure area generated in the interior space defined by the air impeller and creates a low pressure area in the pump inlet. The pump is primed when the liquid material received by the tank is drawn through the pump inlet and into the pump interior